I don't believe so, the best option you have is to use the `-display host:display.screen` command line option.
With this, you could invoke another X session with `startx -- :#` in another virtual terminal (ALT + CONTROL + F2-F6), where # is the number of the display (0 being the default F7, you would start with 1 through 5). With this, you could password one session and leave the rest open.
Sorry I couldn't give you the answer you wanted, hope that helps.
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